Carbocyclic ring closure of hex-5-enopyranosides and pent-4-enofuranosides: a nitrile oxide approach

Nitrile oxide cycloadditions to protected enopyrano(furano)sides derived from D-glucose and D-ribose afford spiro-isoxazolines in good yield and high diastereoselectivity, which upon Raney Nickel hydrogenation in MeOH–AcOH (6∶1) undergo N–O bond cleavage followed by spontaneous aldol-like condensation to give good yields of hydroxylated six- and five-membered cyclic enaminones as the main products.